Using a Burke-Schumman modeled co-flow burner, a quartz chimney, and a pressure vessel with good optical access, the smoke points in pure and diluted fuels were measured in a laminar jet diffusion flame. Ethylene and methane, burning in a velocity matched, over-ventilated co-flow of air, were tested over the ranges of 1 to 8 atmospheres and 2 to 16 atmospheres, respectively. Various diluents (nitrogen, argon, helium, and carbon dioxide) were added individually to the pure fuels to observe the effects they have on the smoke points and the adiabatic flame temperatures at atmospheric and elevated pressures. These diluents were chosen to allow a wide range of flame temperatures and fuel Lewis numbers to be investigated. For a given fuel flow rate, the dilution level was increased until the flame ceased emitting visible soot (defined as the smoke point). The height of the flame was then measured and the adiabatic flame temperature was calculated based on equilibrium chemistry. While some previous research has focused on the effects of flame temperature (through dilution) on smoke points, the measurements reported here were made to investigate the effects of pressure, different diluents, and varying dilution rates on sooting tendency. The main findings of these experiments were: increasing the amount of diluent to a pure fuel increases the smoke point, the smoke point is a function of the air to fuel velocity ratio, smoke point is strongly dependent on the inverse of pressure, and residence time decreases with increases in pressure.